What is this voltage drop tool used for?
This tool calculates the voltage loss for a selected copper or aluminum conductor cross-section, the resulting percent drop and the voltage remaining at the end of the run.
It is useful for checking internal wiring, motor feeder circuits and remote field panels to confirm a chosen cross-section is adequate.
Formula used
- General: ΔU = k x I x L x ρ / A
- For single-phase and DC, k = 2 (outgoing and return conductor)
- For three-phase, k = √3
Variables and meaning
- I
- Line current.
- L
- One-way cable length.
- ρ
- Conductor resistivity (approximate values at 20°C: copper 0.0175, aluminum 0.028 Ω·mm²/m).
- A
- Conductor cross-sectional area.
- k
- Return-conductor or three-phase factor depending on system type.
- ΔU
- Calculated voltage drop.
Unit reference tables
Voltage units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Millivolt (mV) | mV | 0.001 V | Sensors and low-level signals |
| Volt (V) | V | 1 V | Base SI voltage unit |
| Kilovolt (kV) | kV | 1,000 V | High-voltage transmission |
Current units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Milliampere (mA) | mA | 0.001 A | Electronic circuit currents |
| Ampere (A) | A | 1 A | Base SI current unit |
| Kiloampere (kA) | kA | 1,000 A | Industrial power systems |
Length units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Millimeter (mm) | mm | 0.001 m | Thin layers and small diameters |
| Centimeter (cm) | cm | 0.01 m | Short dimensions |
| Meter (m) | m | 1 m | Base SI length unit |
| Kilometer (km) | km | 1,000 m | Very large distances and long layers |
| Inch (in) | in | 0.0254 m | Imperial/US thickness measurements |
| Foot (ft) | ft | 0.3048 m | Imperial/US length measurements |
Cross-section units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Square millimeter (mm²) | mm² | 0.000001 m² | Small sections and surfaces |
| Square centimeter (cm²) | cm² | 0.0001 m² | Medium-scale test surfaces |
| Square meter (m²) | m² | 1 m² | Base SI area unit |
| Square kilometer (km²) | km² | 1,000,000 m² | Very large surfaces |
| Square inch (in²) | in² | 0.00064516 m² | Imperial/US small surface areas |
| Square foot (ft²) | ft² | 0.09290304 m² | Imperial/US surface areas |
Worked examples
400 V, 20 A, 50 m, 6 mm², copper, three-phase
ΔU = 1.732 x 20 x 50 x 0.0175 / 6 which gives about 5.05 V, a 1.26% drop. The end-of-line voltage is about 394.95 V.
230 V, 16 A, 30 m, 2.5 mm², copper, single-phase
ΔU = 2 x 16 x 30 x 0.0175 / 2.5 which gives about 6.72 V, a 2.92% drop. The end-of-line voltage is about 223.28 V.
Typical applications
- Internal wiring checks
- Motor feeder circuits
- Remote sensor or field-panel runs
- Confirming whether an existing cross-section is adequate at a given distance
Assumptions and limitations
- This calculation covers resistive voltage drop only; reactance (inductive drop), harmonics and starting currents are not included.
- The resistivity values used (copper 0.0175, aluminum 0.028 Ω·mm²/m) are approximate 20°C reference values; actual conductor temperature affects the result.
- This tool does not check current-carrying capacity (ampacity). Verify the chosen cross-section separately against the installation method, ambient temperature and applicable electrical code.